Bottom loaded pedicle screw

ABSTRACT

A pedicle screw includes a tulip head, a rod seat, a screw shank, and a retainer collar. The tulip head has an upper opening disposed in a top end of the tulip head and a lower opening disposed in a bottom end of the tulip head opposite the upper opening. The upper and lower openings form a single cavity extending through the tulip head from a top end to the bottom end. The rod seat is disposed within the cavity of the tulip head and engages a stop extending inwardly from an interior wall of the cavity. The screw shank has a thread disposed along a length of the screw shank and a connector positioned at an upper end. The retainer collar has a pass through aperture, an expansion slit, and is disposed about the connector of the screw shank. Other embodiments are described and claimed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/630,703, entitled “BOTTOM LOADED PEDICLE SCREW”, filed Jun. 22, 2017,which is a division of U.S. application Ser. No. 15/219,677, entitled“BOTTOM LOADED PEDICLE SCREW”, filed Jul. 26, 2016 and now U.S. Pat. No.9,820,782, which is a continuation of International Application No.PCT/US2015/035629, entitled “BOTTOM LOADED PEDICLE SCREW”, filed Jun.12, 2015, which claims the benefit of Provisional U.S. Application No.62/127,595, entitled “BOTTOM LOADED PEDICLE SCREW”, filed Mar. 3, 2015,and Provisional U.S. Application No. 62/011,865, entitled “BOTTOM LOADEDPEDICLE SCREW”, filed Jun. 13, 2014, each of which is herebyincorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be more easily understood with reference tothe figures, which are as follow:

FIG. 1A is a side elevational view of an embodiment of a pedicle screwaccording to one or more embodiments;

FIG. 1B is a cross sectional view of the pedicle screw of FIG. 1A, takenalong N-N;

FIG. 2A is a side elevational view of a screw shank of FIG. 1A;

FIG. 2B is a front view of the screw shank of FIG. 2A;

FIG. 2C is a bottom plan view of the screw shank of FIG. 2A;

FIG. 2D is a top plan view of the screw shank of FIG. 2A;

FIG. 3A is an isometric view of a retainer collar of FIG. 1A;

FIG. 3B is a top plan view of the retainer collar of FIG. 3A;

FIG. 3C is a bottom plan view of the retainer collar of FIG. 3A;

FIG. 3D is a right side elevational view of the retainer collar of FIG.3A;

FIG. 3E is a front view of the retainer collar of FIG. 3A;

FIG. 4A is an isometric view of one half of the retainer collar of FIG.3A;

FIG. 4B is a ride side elevational view of the one halve of the retainercollar of FIG. 4A;

FIG. 5A is an isometric view of a tulip head of FIG. 1A;

FIG. 5B is a bottom plan view of the tulip head of FIG. 5A;

FIG. 5C is a top plan view of the tulip head of FIG. 5A;

FIG. 5D is a cross sectional view of the tulip head of FIG. 5A;

FIG. 5E is a cross section view of the tulip head of FIG. 5A;

FIG. 5F is a cross section view of the tulip head of FIG. 5A, takenlaterally across the tulip head of FIG. 5A along the retention groove;

FIG. 6A is an isometric view of a locking ring of FIG. 1A;

FIG. 6B is a top plan view of the locking ring of FIG. 6A, wherein thelocking ring is in an unloaded state;

FIG. 6C is a right side elevational view of the locking ring of FIG. 6A;

FIG. 6D is a cross section view of the locking ring of FIG. 6B, takenalong line P-P;

FIG. 6E is a top plan view of the locking ring of FIG. 6A, wherein thelocking ring is in a loaded state;

FIG. 7A is an isometric view of a rod seat of FIG. 1A;

FIG. 7B is bottom plan view of the rod seat of FIG. 7A;

FIG. 7C is a right side elevational view of the rod seat of FIG. 7A;

FIG. 7D is a front view of the rod seat of FIG. 7A;

FIG. 7E is a top plan view of the rod seat of the FIG. 7A;

FIG. 7F is a cross sectional view of the rod seat of FIG. 7A;

FIG. 8A is a partial isometric view of another embodiment of a screwshank of FIG. 1A;

FIG. 8B is a side elevational view of the screw shank of FIG. 8A withthe rod seat of FIG. 7A coupled thereon;

FIG. 8C is a top plan view of the screw shank of FIG. 8A;

FIG. 9A is a side elevational view of another embodiment of a pediclescrew according to one or more embodiments;

FIG. 9B is a cross sectional view of the pedicle screw of FIG. 9A, takenalong line N-N;

FIG. 10A is a isometric view of another embodiment of a retainer collarof FIG. 1A;

FIG. 10B is top plan view of the retainer collar of FIG. 10A;

FIG. 10C is a bottom plan view of the retainer collar of FIG. 10A;

FIG. 10D is a right side elevational view of the retainer collar of FIG.10A;

FIG. 10E is front view of the retainer collar of FIG. 10A;

FIG. 11 is an isometric view of a locking ring of FIG. 1A;

FIG. 12 is a partial isometric view of another embodiment of a screwshank of FIG. 1A;

FIG. 13A is a side elevational view of the screw shank of FIG. 12;

FIG. 13B is a top plan view of the screw shank of FIG. 13A;

FIG. 13C is a bottom plan view of another embodiment of a retainercollar of FIG. 10A;

FIG. 13D is an isometric view of the screw shank of FIG. 13A with theretainer collar of FIG. 13C coupled thereon;

FIG. 14 is an isometric view of another embodiment of a pedicle screwaccording to one or more embodiment;

FIG. 15 is an exploded view of the pedicle screw of FIG. 14;

FIG. 16 is an isometric view of a retainer collar of FIG. 14;

FIG. 17 is a side elevational view of the retainer collar of FIG. 16;

FIG. 18 is a bottom plan view of the retainer collar of FIG. 16;

FIG. 19 is an isometric view of a tulip head of FIG. 14;

FIG. 20 is a bottom plan view of the tulip head of FIG. 19;

FIG. 21 is an isometric view of a rod seat of FIG. 14;

FIG. 22 is a front view of the rod seat of FIG. 21;

FIG. 23 is a side elevational view of the pedicle screw of FIG. 14;

FIG. 24 is a partial cross sectional view of the pedicle screw of FIG.23, taken along line O-O;

FIG. 25 is a side elevational view of the pedicle screw of FIG. 14;

FIG. 26 is a partial cross sectional view of the pedicle screw of FIG.25, taken along line P-P; and

FIG. 27 is a bottom plan view of the pedicle screw of FIG. 14.

DETAILED DESCRIPTION

The following text sets forth a broad description of numerous differentembodiments. The description is to be construed as exemplary only anddoes not describe every possible embodiment since describing everypossible embodiment would be impractical, if not impossible, and it willbe understood that any feature, characteristic, component, composition,ingredient, product, step or methodology described herein can bedeleted, combined with or substituted for, in whole or part, any otherfeature, characteristic, component, composition, ingredient, product,step or methodology described herein. Numerous alternative embodimentscould be implemented, using either current technology or technologydeveloped after the filing date of this patent, which would still fallwithin the scope of the claims.

It should also be understood that, unless a term is expressly defined inthis specification using the sentence “As used herein, the term ‘______’is hereby defined to mean . . . ” or a similar sentence, there is nointent to limit the meaning of that term, either expressly or byimplication, beyond its plain or ordinary meaning, and such term shouldnot be interpreted to be limited in scope based on any statement made inany section of this patent (other than the language of the claims). Noterm is intended to be essential unless so stated. To the extent thatany term recited in the claims at the end of this patent is referred toin this patent in a manner consistent with a single meaning, that isdone for sake of clarity only so as to not confuse the reader, and it isnot intended that such a claim term be limited, by implication orotherwise, to that single meaning. Finally, unless a claim element isdefined by reciting the word “means” and a function without the recitalof any structure, it is not intended that the scope of any claim elementbe interpreted based on the application of 35 U.S.C. § 112, sixthparagraph.

Embodiments described herein generally relate to a pedicle screw forspinal surgical procedure such as the amelioration and/or correction ofscoliosis or other conditions of the spine wherein the threaded screwshank is loaded into the head from the bottom. A pedicle screw istypically inserted into the area of the vertebrae bones that is betweenthe upper and lower facet joints called the pars articularis or pedicle.

Referring to FIGS. 1A-1C and 9A-B, a pedicle screw 100 is shown. FIG. 1Bis a longitudinal cross sectional view of pedicle screw 100 taken alongsection line, N-N. In the illustrative embodiment shown, pedicle screw100 includes a screw shank 2, retainer collar 4, locking ring 6, tuliphead 8, and rod seat 10. When assembled together, these components formpedicle screw 100. Each of the components set forth above will beindividually described below herein and shown in separate figures. Inaddition, it will be shown and described below herein how each of thecomponents of the pedicle screw 100 are interconnected and, onceassembled, how the pedicle screw 100 works in operation.

Referring to FIGS. 2A-2D and 13A-13B, screw shank 2 of pedicle screw 100is shown. Screw shank 2 comprises at least one helical thread 24 formedalong the length thereof. It is important to note that the proportionsof the bone screw depicted are for illustrative purposes only andvariations in the length of the shank, diameter of the screw, threadpitch, thread length, number of thread leads, shank induced compressionand the like may be varied without departing from the scope of thedisclosure. As will be further described later in this specification,screw shanks of various widths and with various thread sizes arecompatible with the same tulip head 8 reducing the manufacturinginventory. At the upper end of the screw shank 2 is a sphericalconnector 22 having a predetermined diameter. In an embodiment, thespherical connector 22 includes a spherical surface 23 spanning a full360 degrees around the spherical connector 22. Such an arrangement isdeveloped for a poly-axial pedicle screw capable of angulations betweenthe screw shank 2 and the tulip head 8 along multiple axes and is shownin FIGS. 13A-13B, for example. In another embodiment the sphericalconnector 22 includes angulation guides 26 on opposed sides of thespherical connector 22 as illustrated in FIGS. 2A-2B. The angulationguides 26 are planar surfaces formed by removal of the segments of thespherical connector 22 formed by planes intersecting the sphericalconnector 22 on opposed sides circumferentially offset 180°. Such anarrangement is developed for a uni-axial pedicle screw capable ofangulation between the screw shank 2 and the tulip head 8 along a singleaxis. A shank collar 30 connects the spherical connector 22 and thehelical threaded portion. The shank collar 30 is a section of the screwshank 2 of reduced diameter which transitions between the sphericalconnector 22 and the threaded portion of the screw shank 2. The shankcollar 30 provides clearance between the tulip head 8 and the helicalthread 24. In an embodiment, the diameter of the shank collar 30 isapproximately the same as the minor diameter of the helical thread 24.Further, a driver receptacle 28 is located along the upper end of thespherical connector 22 for use in installing the pedicle screw 100 byuse of a driving tool. It should be noted that the driver receptacle 28may be any shape, male or female, suitable for cooperation with adriving tool to rotate the pedicle screw 100 into its final position.

The spherical connector 22 of the screw shank 2 has multiple geometries.In an embodiment, the spherical connector 22 is smooth without ridges orother surface perturbances as shown in FIGS. 2A and 2B for example.Specifically, the spherical portion of the spherical connector 22maintains a spherical geometry within the bounds of normal machining ormanufacturing variances. In another embodiment, the spherical connector22 comprises surface perturbances 25 as shown in FIG. 12 for example. Invarious embodiments, the surface perturbances are ridges, grooves, orsurface roughness. The perturbances may be formed in a vertical,horizontal, radial, crosshatched, circular, isotropic arrangement on thespherical connector 22 surface. The surface protuberances provideincreased friction and/or adhesion between the screw shank 2, theretainer collar 4, and the rod seat 10.

Referring to FIGS. 3A-3E, 4A-4B, and 10A-10E, retainer collar 4 ofpedicle screw 100 is shown. In various embodiments, the retainer collar4 comprises two semicircular collar halves 4 a/4 b which combine to forma partial or full annular profile. In various other embodiments, theretainer collar 4 comprises a singular annular structure with a collarexpansion split 54 disposed therein to allow expansion of the retainercollar 4. As shown, the retainer collar 4 has an outer diameter (D_(CO))in its operational position.

In an embodiment, each segment of the retainer collar 4 includes ananti-rotation tab 32. The anti-rotation tab 32 projects from a topsurface of the retainer collar 4 and is configured to mate with acorresponding anti-rotation socket 90 in the tulip head 8. In auni-axial pedicle screw 100, prevention of rotation of the retainercollar 4 in turn prevents rotation of the screw shank 2 relative totulip head 8. Rotation of screw shank 2 relative to tulip head 8 in auni-axial screw is generally not desirable as the direction of pivotwould also rotate. In an embodiment of a uni-axial pedicle screw 100,anti-rotation tabs 32 are omitted to allow angulation and manipulationof tulip head 8 after insertion of screw shank 2 into a patient's bone.In a poly-axial pedicle screw 100 rotation of the screw shank 2 relativeto the tulip head 8 is not generally a concern so the anti-rotation tabs32 may be omitted or retained.

The retainer collar 4 comprises a locking ring groove 34. The lockingring groove 34 is disposed on the outer surface of the retainer collar 4and forms a recessed channel. In an embodiment, the locking ring groove34 has two side walls 42 and a bottom wall 44 as shown in FIGS. 1B and4B, for example. In another embodiment, the locking ring groove 34 has asemicircular profile as shown in FIGS. 9B and 10A-10E, for example. Thelocking ring groove 34 is sized and configured to accept a locking ring6.

In an embodiment, the interior surface of the retainer collar 4 includesa spherical connector mating surface 36 sized and configured tointerface and mate with the spherical connector 22 of the screw shank 2.In an embodiment, specifically a poly-axial pedicle screw 100, thespherical connector mating surface 36 comprises a curved surfacematching the curved profile of the spherical connector 22 and the curvedprofile extends the full 360° profile of the interior surface of theretainer collar 4 as shown in FIG. 13C. In another embodiment,specifically a uni-axial pedicle screw 100, the spherical connectormating surface 36 comprises a curved surface matching the curved profileof the spherical connector 22 as well as flat planar surfaces 38matching the angulation guides 26 of the spherical connector 22 as shownin FIGS. 3A and 10A. The arrangement of the curved profile and planarsurfaces match the arrangement of the spherical portions and theangulation guides 26 of the spherical connector 22.

In a further embodiment, the retainer collar 4 comprises a shephericalconnector mating edge 52 as shown in FIG. 10A. The spherical connectormating edge 52 interfaces with the spherical connector 22 of the screwshank 2. In an embodiment, the spherical connector mating edge 52comprises a sharp edge which cuts or depresses into the sphericalconnector 22 upon insertion and tightening of a connector rod into thepedicle screw 100.

The retainer collar 4 retains the spherical connector 22 of the screwshank 2. A screw shank pass-through aperture 48 is formed in retainercollar 4. The screw shank pass-through aperture 48 is sized to fitaround the shank collar 30 of the screw shank 2 but prevent passage ofthe spherical connector 22. In an embodiment, the screw shankpass-through aperture 48 is formed by the two semicircular collar halves4 a/4 b when combined together, with each of the two semicircular collarhalves 4 a/4 b forming approximately half of the screw shankpass-through aperture 48. In a further embodiment, wherein retainercollar 4 is a single piece, screw shank pass-through aperture 48 isnaturally formed by the annular configuration of the retainer collar 4.

Referring to FIGS. 5A-5F, one embodiment of the tulip head 8 is shown.Tulip head 8 defines an upper opening 81 and a lower opening 82. Theupper opening 81 and lower opening 82 form a single cavity extendingthrough the tulip head from the top end 83 to the bottom end 84. Thelower opening 82 has a diameter (D_(LO)). Proximate to bottom end 84, aninterior wall of the tulip head 8 comprises a retention groove 86disposed therein. In an embodiment, the retention groove 86 forms arecessed channel with two side walls 87 and a bottom wall 88 asillustrated in FIGS. 1B and 5D-5E, for example. In another embodiment,the retention groove 86 forms a semicircular channel as shown, forexample, in FIGS. 9B and 10D-10E. The retention groove 86 is sized andconfigured to accept the locking ring 6. In the illustrated embodiments,the retention groove 86 extends around the entire perimeter of loweropening 82 as illustrated in FIG. 5F representing a bottom view of tuliphead 8 cut through retention groove 86.

In the illustrated embodiments, tulip head 8 includes a pair ofanti-rotation sockets 90. The anti-rotation sockets are shaped andconfigured to mate with the anti-rotation tabs 32 of the retainer collar4. When the retainer collar 4 is inserted into the lower opening 82 ofthe tulip head 8 the anti-rotation tabs 32 project into theanti-rotation sockets 90 and prevent relative rotational movementbetween the retainer collar 4 and the tulip head 8.

Tulip head 8, in the illustrated embodiment includes a pair of arms 91which define a U-shaped channel 92 transverse to the single openingextending between upper opening 81 and lower opening 82. In anembodiment, internal threads 94 are formed in arms 91. The threadprofile of internal threads 94 may be any profile known to one skilledin the art. Non-limiting examples of internal threads 94 include reverseangle threads, square threads, ACME threads, and buttress threads.

Referring to FIGS. 6A-6D and 11, locking ring 6 of pedicle screw 100 isshown. Locking ring 6 retains the tulip head 8 and the retainer collar 4in an affixed position wherein axial movement is limited. In theillustrated embodiment, locking ring 6 has the form of a C-shaped springor clip having a compression zone 62. The locking ring 6 comprises anannular geometry with a portion removed. The removed portion of theannular geometry forms the compression zone 62. The compression zone 62of the locking ring 6 allows the locking ring 6 to be compressed into areduced diameter arrangement. In the embodiment shown, locking ring 6has an unloaded or natural state with an unloaded outer diameter(D_(O1)) and an unloaded inner diameter (D_(I1)) and a loaded orunnatural state with a loaded outer diameter (D_(O2)) and a loaded innerdiameter (D_(I2)). The unloaded outer diameter (D_(O1)) and unloadedinner diameter (D_(I1)) represent diameters measured when locking ring 6is under no contractive stress (i.e. no reduction in compression zone62) or expansive stress (i.e. no expansion in compression zone 62). Theloaded outer diameter (D_(O2)) and loaded inner diameter (D_(I2))represent diameters measured when locking ring 6 is under a contractivestress (i.e. a reduction in compression zone 62).

The unloaded outer diameter (D_(O1)) is greater than the diameter(D_(LO)) of the lower opening 82 of tulip head 8. This arrangementretains the locking ring in the retention groove 86 when the lockingring 6 is in an unloaded or natural state. Additionally, the loadedouter diameter (D_(O2)) is less than the outer diameter (D_(CO)) of theretainer collar 4. This arrangement retains the locking ring in thelocking ring groove 34 of the retainer collar 4 when the locking ring 6is in an unloaded or natural state.

Referring to FIGS. 7A-7F, an embodiment of rod seat 10 is shown. Rodseat 10 functions to transfer force applied to a spinal rod disposed inthe pedicle screw 100 to the spherical connector 22 of the screw shank2. The rod seat 10 comprises a rod mating face 12 and a shank matingface 14. In an embodiment, the rod seat 10 further comprises a pair ofretention ledges 16.

The rod mating face 12 is configured to accommodate the geometry of anelongated member, with the illustrated embodiment configured to matewith a spinal rod having a circular cross-sectional shape. Alternativelyor additionally, the rod mating face 12 of rod seat 10 can have one ormore other shapes to match elongated member geometries of differingdiameter or shape. The shank mating face 14 is configured to accommodatethe spherical connector 22 of the screw shank 2, and therefore theillustrated embodiment of shank mating face 14 has the shape of part ofa sphere. Alternatively or additionally, the shank mating face 14 of rodseat 10 can have one or more other shapes to match differing sphericalconnector 22 geometries. In an embodiment, shank mating face 14 can beprovided with a friction- or purchase-enhancing surface configuration(e.g. roughening or knurling) for cooperation with spherical connector22 of the screw shank 2.

The illustrated embodiment of rod seat 10 also includes a hole 18disposed therethrough. Hole 18 is provided so that the sphericalconnector 22 and, specifically, the driver receptacle 28, of screw shank2 may be accessed through rod seat 10.

Rod seat 10 is sized and shaped to fit within at least chamber 96 oftulip head 8. The outer diameter of rod seat 10 is preferably slightlysmaller than the inner diameter of chamber 96 and smaller than loweropening 82 so that rod seat 10 is slidably and rotatably movable withinchamber 96 and lower opening 82. Further, in the illustrated embodimentthe outer diameter of rod seat 10 is larger than the inner dimension ofupper opening 81, so that rod seat 10 cannot move into upper opening 81.The cavity 89 such as, for example, chamber 96, may include a stop thatextends inwardly from the interior wall of the cavity 89 sufficientenough to engage a corresponding stop on the rod seat 10 to prevent therod seat from moving into the upper portion of the cavity 89 and/or theupper opening 81. The cavity stop(s) may be disposed above the retentiongroove 86 but below the upper opening 81 and/or upper cavity.Specifically, in the illustrated embodiment, retention ledges 16 (i.e.,stops of the rod seat 10) mate with the upper face of chamber 96 (i.e.,stops of the cavity 89) to prevent movement of rod seat 10 into upperopening 81. It is understood that other embodiments and configurationsof the corresponding stops may be used to prevent the rod seat 10 frommoving into the upper cavity and/or the upper opening. Further, in theillustrated embodiment, the retention ledges 16 mate with arms 91 toprevent rotation of the rod seat 10 relative to the tulip head 8.

Generally referring to FIGS. 1A-1C, 8A-8C, 9A-9B, 12 and 13D, anembodiment of a method of assembling the pedicle screw 100 may generallyinclude assembling rod seat 10 and retainer collar 4 adjacent to and/orpartially or entirely about connector 22 of screw shank 2 and insertinglocking ring 6 into locking ring groove 34 to form a subassembly, andthen subsequently inserting the subassembly into the lower opening 82 ofthe tulip head until the locking ring 6 snaps into and/or engagesretention groove 34.

In some embodiments, the screw shank 2, rod seat 10, retainer collar 4,and locking ring 6 may each be inserted into tulip head 8 individually.For example, the method may include inserting the rod seat 10 into loweropening 82 of tulip head 8 first and then subsequently inserting thelocking ring 6 into lower opening 82 until locking ring 6 snaps intoand/or engages retention groove 86. The method may further includeplacing the retainer collar 4 about a portion of or entirely about theconnector 22, and then subsequently, inserting the retainer collar 4 andscrew shank 2 subassembly into lower end 82 until the locking ring 6snaps into and/or engages locking ring groove 34 of the subassembly.

In another example, a method may include placing retainer collar 4partially or entirely about the spherical connector 22 to form asubassembly, snapping and/or engaging locking ring 6 into locking ringgroove 34 around the retainer collar 4, inserting the rod seat 10 intolower opening 82 of tulip head 8 first and next inserting screw shank 2,retainer collar 4, and locking ring 6 subassembly into lower opening 82until the locking ring engages and/or snaps into the retention groove 86within the cavity of tulip head 8.

In one specific embodiment, retainer collar 4 are fitted around thespherical connector 22 of screw shank 2 and locking ring 6 is fittedinto locking ring groove 34 of retainer collar 4 prior to insertion ofscrew shank 2 into tulip head 8. In an embodiment, retainer collar 4 canbe placed around spherical connector 22 of screw shank 2 by placing thetwo semicircular collar halves 4 a/4 b of retainer collar 4 on opposedsides of the spherical connector 22. In another embodiment, the retainercollar 4 can be placed around spherical connector 22 of screw shank 2 byexpanding the diameter of screw shank pass-through aperture 48 to fitover the spherical connector 22. The multi-piece nature of retainercollar 4 allows screw shank pass-through aperture 48 to be smaller thanspherical connector 22. Locking ring 6 can be placed around retainercollar 4 and screw shank 2 by inserting the spherical connector 22 withthe retainer collar 4 disposed thereon through locking ring pass-throughaperture 64 of locking ring 6. Passage of retainer collar 4 throughlocking ring pass-through aperture 64 causes compression zone 62 toexpand thereby enlarging unloaded inner diameter D_(I1) of locking ring6 to accommodate passage of retainer collar 4. Upon alignment of lockingring 6 with locking ring groove 34, locking ring 6 contracts inwardlyback to its normal state, i.e. compression zone 62 contracts, therebyreducing the inner diameter of locking ring 6 back to its unloaded stateand unloaded diameter D_(I1) and thus securing locking ring 6 intolocking ring groove 34 of retainer collar 4. In an embodiment, retentionof locking ring 6 into locking ring groove 34 also retains the halves ofretainer collar 4 around spherical head 22 of screw shank 2.Subsequently, compression zone 62 of locking ring 6 may be reduced onceagain via compressing locking ring 6 inwardly beyond its normal state(unloaded state), thereby reducing unloaded outer diameter D_(O1) oflocking ring 6. While in a compressed configuration, the assembly oflocking ring 6, retainer collar 4, and screw shank 2 are inserted intotulip head 8 through lower opening 82. Upon alignment of locking ring 6with retention groove 86 of tulip head 8, compression of locking ring 6is allowed to release, locking ring 6 expands, and locking ring 6 issecured into retention groove 86. Securing of locking ring 6 alsoretains retainer collar 4 and screw shank 2 in the tulip head 8.

Alternatively, compression zone 62 of locking ring 6 may be reducedthereby reducing unloaded outer diameter D_(O1) of locking ring 6. Whilein a compressed configuration, locking ring 6 is inserted into tuliphead 8 through lower opening 82. Upon alignment with retention groove 86of tulip head 8, compression of locking ring 6 is allowed to release,locking ring 6 expands back to its unloaded outer diameter D_(O1), andlocking ring 6 is secured into retention groove 86. Subsequently, screwshank 2 having retainer collar 4 disposed around spherical connector 22is inserted into tulip head 8 through lower opening 82. Upon contactwith locking ring 6, the retainer collar 4 forces expansion of theunloaded inner diameter D_(I1) of locking ring 6 such that retainercollar 4 is allowed to pass through. Upon alignment of locking ring 6with locking ring groove 34, compression zone 62 contracts therebyreducing the inner diameter of locking ring 6 back to its unloaded innerdiameter D_(I1) and securing locking ring 6 into locking ring groove 34of retainer collar 4. Securing of retainer collar 4 by the locking ring6 also retains screw shank 2 in the tulip head 8.

Prior to insertion of the screw shank 2, retainer collar 4, or lockingring 6 into the tulip head 8, rod seat 10 is inserted into tulip head 8through lower opening 82. Rod seat 10 remains slideably and rotatablypositioned in chamber 96 of tulip head 8, and screw shank 2 remainsmoveable with respect to tulip head 8 and rod seat 10. Movement of screwshank 2 in a poly-axial or uni-axial manner in relation to tulip head 8and rod seat 10 depends on the configuration of spherical connector 22.In a poly-axial arrangement of spherical connector 22, where sphericalconnector 22 retains a curved profile around the entire periphery, thescrew shank 2 may move in a poly-axial manner. In a uni-axialarrangement of spherical connector 22, where spherical connector 22 hasflat angulation guides 26, the screw shank 2 may move in a uni-axialmanner. However, in poly-axial configurations and uni-axialconfigurations without anti-rotation tabs 32 on the retainer collar 4,screw shank 2 may rotate about a longitudinal axis of the screw shank 2relative to the tulip head 8.

In one specific embodiment the diameter of retention groove 86 of tuliphead 8 is smaller than the unloaded outer diameter D_(O1) of lockingring 6 in its natural (i.e., unloaded) state. Thus, when locking ring 6is within retention groove 86, locking ring 6 is continually under acompressive force and presses against the bottom wall 88 of retentiongroove 86. Alternatively, the diameter of retention groove 86 may be thesame size or slightly larger than the unloaded outer diameter D_(O1) oflocking ring 6. If the diameter of retention groove 86 is the same sizeor slightly larger than the unloaded outer diameter D_(O1) of lockingring 6, locking ring 6 rests upon a side wall 87 of retention groove 86which holds locking ring 6 within retention groove 86. The depth ofretention groove 86 is less than the width of locking ring 6, so thatwhen locking ring 6 is disposed in retention groove 86, a portion oflocking ring 6 projects into chamber 96 proximal to lower opening 82. Insome embodiments, the width of locking ring 6 is equivalent to thedifference between the unloaded outer diameter D_(O1) and the unloadedinner diameter D_(I1).

When locking ring 6 is seated within retention groove 86 and lockingring groove 34, screw shank 2 and rod seat 10 are retained within loweropening 82 of tulip head 8. Rod seat 10 is supported by sphericalconnector 22 of screw shank 2, and spherical connector 22 is supportedby spherical connector mating surfaces 36 of retainer collar 4. In anembodiment, retainer collar 4 is held around spherical connector 22 bylocking ring 6 disposed in locking ring groove 34. Locking ring 6 isheld by retention groove 86 of tulip head 8 and, thus, screw shank 2,retainer collar 4, and rod seat 10 are held in tulip head 8.

Preferably, pedicle screw 100 is assembled (as described above) prior touse in a surgical procedure. Alternatively, it is envisioned that all ora portion of assembly may be completed in the operating theater. Thebottom loading aspect of the assembly wherein the screw shank 2 isinserted into the tulip head 8 through lower opening 82 allows the sametulip head 8 to be used for screw shanks 2 of various thread diameterand/or pitch. A standard dimension of the spherical connector 22 isutilized for screw shanks 2 of different diameters and because thethreaded portion of the screw shank 2 does not have to pass throughtulip head 8 the geometry of tulip head 8 may be consistent.

The bottom loading configuration of pedicle screw 100 during theassembly process also allows for an overall lower profile tulip head 8.

In using the illustrated embodiment of pedicle screw 100, screw shank 2of pedicle screw 100 is threaded into an appropriately prepared hole ina bone (not shown). The threaded portion of screw shank 2 is insertedinto the hole, and an appropriate screwing tool is used with driverreceptacle 28 of screw shank 2 through hole 18 in rod seat 10, and screwshank 2 is threaded into the bone. When screw shank 2 has been threadedinto the bone to the desired depth, tulip head 8 is positioned so thatupper opening 81 forms a desired angle with screw shank 2 and U-shapedchannel 92 is oriented in the desired direction. An elongated membersuch as a spinal rod, connector, or other orthopedic surgical implant iscoupled with pedicle screw 100 by placing the elongated member inU-shaped channel 92 of tulip head 8 such that it contacts rod matingface 12 of rod seat 10. A compression member, such as a set screw orthreaded plug, is threaded into internal threads 94 of tulip head 8 tosecure the elongated member. As the compression member is tightened,elongated member is forced downward against rod seat 10, which pushesshank mating face 14 of rod seat 10 down onto spherical connector 22 ofscrew shank 2. Spherical connector 22 is thereby clamped between shankmating face 14 of rod seat 10 and spherical connector mating surface 36or spherical connector mating edge 52 of retainer collar 4. In this way,screw shank 2 is locked into the desired angular position with respectto elongated member and the remainder of pedicle screw 100.

Referring to FIGS. 14-27, another embodiment of a pedicle screw 200 isshown. The pedicle screw 200 includes a screw shank 2, retainer collar204, locking ring 206, tulip head 208, and rod seat 210. When assembledtogether, these components form pedicle screw 200. Each of thecomponents set forth above will be individually described below hereinand, in some cases, shown in separate figures. In addition, it will beshown and described below herein how each of the components of thepedicle screw 200 are interconnected and, once assembled, how thepedicle screw 200 works in operation. In this embodiment, the screwshank 2 is the same as the screw shank 2 described above herein andshown, for example, in FIGS. 2A-2D and 13A-13B, which is herebyincorporated by reference herein.

Referring to FIG. 15, locking ring 206 of pedicle screw 200 is shown.Locking ring 206 in this embodiment is a wire formed into an annularring having a locking ring pass-through aperture 264. As shown, thelocking ring 206 includes a gap 261 between opposite ends of the wire.The wire may be fabricated from a variety of metals, alloys, and/orcomposites. In one example, the wire is fabricated from cobalt-chromium(CoCr) or the like, including but not limited tocobalt-chromium-molybdenum (CoCrMo), cobalt-nickel-chromium-molybdenum(CoNiCrMo). In some examples, the locking ring 206 is fabricated formmaterials such as, for example, metal alloys with high wear-resistanceand biocompatibility.

Referring to FIGS. 16-18, retainer collar 204 of pedicle screw 200 isshown. In various embodiments, the retainer collar 204 comprises anannular body 241 having a collar split 254 that may or may not allow theannular body to expand and/or contract in its diameter. In someembodiments, the retainer collar 204 may comprise embodiments as shownand described above herein such as, for example, retainer collar 4. Inthe embodiment shown in FIGS. 16-18, the retainer collar 204 includes alocking ring groove 234 disposed within an outer surface of annular body241. The locking ring groove 234 is shown as disposed continuouslyaround the annular body 241, forming a recessed channel. In thisembodiment, locking ring groove 234 has a semicircular profile. However,it is understood that locking ring groove 234 does not need to becontinuous or completely encircle the annular body 241. In addition,locking ring groove 234 may comprise a variety of shapes, sizes,configurations, profiles, and designs, but is generally shaped and sizedto accept locking ring 206.

The annular body 241 also includes anti-rotation tabs 232 a, 232 c, 232e, and 232 g and anti-rotation tabs 232 b, 232 d, 232 f, and 232 h thatare disposed on a side of the locking ring groove 234 opposite fromanti-rotation tabs 232 a, 232 c, 232 e, and 232 g, respectively. Asshown, the anti-rotation tabs 232 a-h radially project from the annularbody 241 and are configured to mate with corresponding anti-rotationsockets 290 a-h, respectively, disposed in the tulip head 208 as will bedescribed below herein.

In a uni-axial pedicle screw 200, prevention of rotation of the retainercollar 204 in turn prevents rotation of the screw shank 2 relative totulip head 208. Rotation of screw shank 2 relative to tulip head 208 ina uni-axial screw is generally not desirable as the direction of pivotwould also rotate. In an embodiment of a uni-axial pedicle screw 200,anti-rotation tabs 232 a-h are omitted to allow angulation andmanipulation of tulip head 208 after insertion of screw shank 2 into apatient's bone. In a poly-axial pedicle screw 200 rotation of the screwshank 2 relative to the tulip head 208 is not generally a concern so theanti-rotation tabs 232 a-h may be omitted or retained.

In an embodiment, the interior surface of the retainer collar 204includes a spherical connector mating surface 236 sized and configuredto interface and mate with the spherical connector 22 of the screw shank2. In an embodiment, specifically a poly-axial pedicle screw 200, thespherical connector mating surface 236 comprises a curved surfacematching the curved profile of the spherical connector 22 and the curvedprofile extends the full 360° profile of the interior surface of theretainer collar 204. In another embodiment, specifically a uni-axialpedicle screw 200, the spherical connector mating surface 236 comprisesa curved surface matching the curved profile of the spherical connector22 as well as flat planar surfaces 238 matching the angulation guides 26of the spherical connector 22 as shown in FIGS. 16, 18, 24, and 26. Thearrangement of the curved profile and planar surfaces match thearrangement of the spherical portions and the angulation guides 26 ofthe spherical connector 22.

The retainer collar 204 retains the spherical connector 22 of the screwshank 2. A screw shank pass-through aperture 248 is formed in retainercollar 204. The screw shank pass-through aperture 248 is sized to fitaround the shank collar 30 of the screw shank 2 but prevent passage ofthe spherical connector 22. In an embodiment, the screw shankpass-through aperture 248 is formed by the annular body 241 of theretainer collar 204. In some embodiments, the retainer collar 204 maycomprise a spherical connector mating edge such as, for example, matingedge 52 described above herein and shown in FIG. 10A.

Referring to FIGS. 19-20, one embodiment of the tulip head 208 is shown.Tulip head 208 defines an upper opening 281 and a lower opening 282. Theupper opening 281 and lower opening 282 form a single cavity extendingfrom the top end 283 to the bottom end 284. Proximate to bottom end 284,the tulip head 208 comprises a retention groove 286. In this embodiment,retention groove 286 has a semicircular profile as illustrated in FIGS.19, 24, and 26, for example. In another embodiment, the retention groove86 may include two side walls and a bottom wall such as, for example,those shown and described above herein with reference to FIGS. 5D-5E.The retention groove 286 is sized and configured to accept the lockingring 206. In the illustrated embodiments, the retention groove 286extends around the entire perimeter of lower opening 282 and is incommunication and/or connected with a retention groove inlet 287 thatextends to an exterior surface of the tulip head 208. The retentiongroove inlet 287 is configured and sized to accept and/or receive thelocking ring 206 and permit the locking ring 206 to travel therethroughand enter into the retention groove 286.

In the illustrated embodiments, tulip head 208 includes a pair ofanti-rotation sockets 290 a-h. The anti-rotation sockets 290 a-h areshaped and configured to mate with the respective anti-rotation tabs 232a-h of the retainer collar 204. When the retainer collar 204 is insertedinto the lower opening 282 of the tulip head 208 the anti-rotation tabs232 a-h project into the respective anti-rotation sockets 290 a-h andprevent relative rotational movement between the retainer collar 204 andthe tulip head 208.

Tulip head 208, in the illustrated embodiment includes a pair of arms291 which define a U-shaped channel 292 transverse to the single openingextending between upper opening 281 and lower opening 282. In anembodiment, internal threads 294 are formed in arms 291. The threadprofile of internal threads 294 may be any profile known to one skilledin the art. Non-limiting examples of internal threads 294 includereverse angle threads, square threads, ACME threads, and buttressthreads. These threads 294 may be configured to receive and threadinglyengage an externally threaded set screw. In an embodiment, each arm 291of the tulip head 208 further includes a tulip head pocket 270 as shown,for example, in FIGS. 14, 19, and 26. In the embodiment shown, the tuliphead pockets 270 of the tulip head 208 do not extend transversely allthe way across the tulip head 208. Thus, in this illustrativeembodiment, the tulip head pockets 270 each have an upper wall 272 thatincludes a tulip head undercut 273, a lower wall 274, two opposed sidewalls 276, and a back wall 278 disposed between the two opposed sidewalls 276. In an embodiment, the tulip head pockets 270 and, morespecifically, the tulip head undercuts 273 are constructed to engagevarious orthopedic surgical tools configured to facilitate installation,removal, and/or adjustment of the pedicle screw 200.

Referring to FIGS. 21-22, an embodiment of rod seat 210 is shown. Rodseat 210 functions to transfer force applied to a spinal rod (not shown)disposed in the U-shaped channel 292 of pedicle screw 200 to thespherical connector 22 of the screw shank 2. The rod seat 210 comprisesa rod mating face 212 and a shank mating face 214. In an embodiment, therod seat 210 further comprises a pair of retention ledges 216.

The rod mating face 212 is configured to accommodate the geometry of anelongated member, with the illustrated embodiment configured to matewith a spinal rod having a circular cross-sectional shape. Alternativelyor additionally, the rod mating face 212 of rod seat 210 may have one ormore other shapes to match elongated member geometries of differingdiameter or shape. The shank mating face 214 is configured toaccommodate the spherical connector 22 of the screw shank 2, andtherefore the illustrated embodiment of shank mating face 214 has theshape of a portion of a sphere. Alternatively or additionally, the shankmating face 214 of rod seat 210 may have one or more other shapes tomatch differing spherical connector 22 geometries. In an embodiment,shank mating face 214 may be provided with a friction- orpurchase-enhancing surface configuration (e.g. roughening or knurling)for cooperation with spherical connector 22 of the screw shank 2.

The illustrated embodiment of rod seat 210 also includes a hole 218disposed therethrough. Hole 218 is provided so that the sphericalconnector 22, and specifically, the driver receptacle 28, of screw shank2 may be accessed through rod seat 210. Rod seat 210 is sized and shapedto fit within at least chamber 296 of tulip head 208. The outer diameterof rod seat 210 is preferably slightly smaller than the inner diameterof chamber 296 and smaller than lower opening 282 so that rod seat 210is slidably and rotatably movable within chamber 296 and lower opening282. Further, in the illustrated embodiment the outer diameter of rodseat 210 is larger than the inner dimension of upper opening 281, sothat rod seat 210 cannot move into upper opening 281. Specifically, inthe illustrated embodiment, retention ledges 216 mate with the upperface of chamber 296 to prevent movement of rod seat 210 into upperopening 281. Further, in the illustrated embodiment, the retentionledges 216 mate with arms 291 to prevent rotation of the rod seat 210relative to the tulip head 208.

Generally referring to FIGS. 14-27, pedicle screw 200 is assembled asfollows: screw shank 2, rod seat 210, and retainer collar 204 areinserted into tulip head 208 through bottom end 284. The screw shank 2,rod seat 210, and retainer collar 204 may be inserted into tulip head208 either individually or substantially in a single step. For example,the rod seat 210 may be inserted into the bottom end 284 of tulip head208 first, followed by screw shank 2, and then the retainer collar 204may be slid around the spherical connector 22 and into the bottom end284 of the tulip head 208. Alternatively, the rod seat 210 may beinserted into tulip head 208 first, followed by screw shank 2 withretainer collar 204 which has been already placed around the sphericalconnector 22. In either embodiment, after the rod seat 210, screw shank2, and retainer collar 204 have been assembled and inserted into thebottom end 284 of the tulip head 208, the locking ring groove 234 ofretainer collar 204 aligns and/or mates with retention groove 286 oftulip head 208 to form an annular channel about the bottom end 284. Oncethese components are assembled together as set forth above, the lockingring 206 may be inserted into the retention groove inlet 287 and intoand around the channel formed from the locking ring groove 234 andretention groove 286. As set forth above, in some embodiments, thelocking ring 206 is a wire. A sufficient length of wire is inserted intothe retention groove inlet 287 and subsequently into and around thechannel formed from the combination of the locking ring groove 234 andretention groove 286 in order to hold or lock the assembly to and withinthe tulip head 208. In some embodiments, the wire 206 is part of a spoolof wire and thus when a sufficient length of the wire is inserted intothe channel formed from the locking ring groove 234 and retention groove286, the wire may be severed from the remainder of the spool outside thetulip head 208, within the retention groove inlet 287 or within theretention groove 286 itself.

As set forth above, prior to insertion of the screw shank 2 and/orretainer collar 204 into the tulip head 208, rod seat 210 is insertedinto tulip head 208 through lower opening 282. Rod seat 210 remainsslideably and rotatably positioned in chamber 296 of tulip head 208, andscrew shank 2 remains moveable with respect to tulip head 208 and rodseat 210. Movement of screw shank 2 in a poly-axial or uni-axial mannerin relation to tulip head 208 and rod seat 210 depends on theconfiguration of spherical connector 22. In a poly-axial arrangement ofspherical connector 22, where spherical connector 22 retains a curvedprofile around the entire periphery (approximately 360 degrees), thescrew shank 2 may move in a poly-axial manner. In a uni-axialarrangement of spherical connector 22, where spherical connector 22 hasflat angulation guides 26, the screw shank 2 may move in a uni-axialmanner. However, in poly-axial configurations and uni-axialconfigurations without anti-rotation tabs 232 a-h on the retainer collar204, screw shank 2 may rotate about a longitudinal axis of the screwshank 2 relative to the tulip head 208.

As set forth above, when locking ring 206 is seated within retentiongroove 286 and locking ring groove 234, screw shank 2, retainer collar204, and rod seat 210 are retained within lower opening 282 of tuliphead 208. Rod seat 210 is supported by spherical connector 22 of screwshank 2, and spherical connector 22 is supported by spherical connectormating surfaces 236 of retainer collar 204. In an embodiment, retainercollar 204 is held around spherical connector 22 by locking ring 206disposed in locking ring groove 234. Locking ring 206 is held byretention groove 286 of tulip head 208 and thus screw shank 2, retainercollar 204, and rod seat 210 are held in tulip head 208.

In some embodiments, pedicle screw 200 is assembled (as described above)prior to use in a surgical procedure. In some embodiments, it isenvisioned that all or a portion of assembly may be completed in theoperating theater. The bottom loading aspect of the assembly wherein thescrew shank 2 is inserted into the tulip head 208 through lower opening282 allows the same tulip head 208 to be used for screw shanks 2 ofvarious thread diameter and/or pitch. A standard dimension of thespherical connector 22 is utilized for screw shanks 2 of differentdiameters and because the threaded portion of the screw shank 2 does nothave to pass through tulip head 208 the geometry of tulip head 208 maybe consistent.

The bottom loading configuration of pedicle screw 200 during theassembly process also allows for an overall lower profile tulip head208.

In using the illustrated embodiment of pedicle screw 200, screw shank 2of pedicle screw 200 is threaded into an appropriately prepared hole ina bone (not shown). The threaded portion of screw shank 2 is insertedinto the hole, and an appropriate driving/screwing tool is used withdriver receptacle 28 of screw shank 2 through hole 218 in rod seat 210,and screw shank 2 is threaded into the bone. When screw shank 2 has beenthreaded into the bone to the desired depth, tulip head 208 ispositioned so that upper opening 281 forms a desired angle with screwshank 2 and U-shaped channel 292 is oriented in the desired direction.An elongated member such as a spinal rod, connector, or other orthopedicsurgical implant is coupled with pedicle screw 200 by placing theelongated member in U-shaped channel 292 of tulip head 208 such that itcontacts rod mating face 212 of rod seat 210. A compression member, suchas a set screw or threaded plug, is threaded into internal threads 294of tulip head 208 to secure the elongated member. As the compressionmember is tightened, elongated member is forced downward against rodseat 210, which pushes shank mating face 214 of rod seat 210 down ontospherical connector 22 of screw shank 2. Spherical connector 22 isthereby clamped between shank mating face 214 of rod seat 210 andspherical connector mating surface 36 of retainer collar 204. In thisway, screw shank 2 is locked into the desired angular position withrespect to elongated member and the remainder of pedicle screw 200.

Illustrative materials for use in one or more components of the pediclescrews shown and described herein include, but are not limited to,stainless steel, titanium, titanium alloys, and cobalt-chromium alloyssuch as, for example, cobalt-chromium-molybdenum alloys. It will berecognized that any sturdy biocompatible material may be used for one ormore embodiments shown and described herein or any one or more of thesubcomponents of these embodiments.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany embodiment disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present disclosure have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made. It istherefore intended to cover in the appended claims all such changes andmodifications.

The invention claimed is:
 1. A pedicle screw comprising: a tulip headhaving an upper opening disposed in a top end of the tulip head and alower opening disposed in a bottom end of the tulip head opposite theupper opening, wherein: the upper and lower openings form a singlecavity extending through the tulip head from the top end to the bottomend, and the cavity has an interior wall, internal threads disposedwithin the interior wall and adjacent to the upper opening, and a stopdisposed between the lower opening and the upper opening, the stopextending substantially at right angles inwardly from the interior walland separate from the internal threads; a rod seat disposed within thecavity and engageable with the stop, the rod seat having a rod matingface, a shank mating face opposite the rod mating face, and a holedisposed through the rod mating face and shank mating face; a screwshank having a thread disposed along a length of the screw shank and aconnector positioned at an upper end of the screw shank; a retainercollar having a collar body, a pass through aperture disposed throughthe collar body, an anti-rotation tab extending from the collar body,and a collar expansion split disposed within the collar body, whereinthe retainer collar is disposed about the connector of the screw shank;and wherein the cavity of the tulip head further includes ananti-rotation socket constructed to receive and engage the anti-rotationtab of the retainer collar.
 2. The pedicle screw according to claim 1,wherein: the cavity of the tulip head has a retention groove disposedwithin the interior wall; the stop is disposed between the retentiongroove and the upper opening; and the retainer collar has a locking ringgroove disposed within an outer surface of the collar body.
 3. Thepedicle screw according to claim 2, further comprising a locking ringdisposed within the retention groove and the locking ring groove.
 4. Thepedicle screw according to claim 3, wherein the locking ring has acompression zone disposed therein such that when the compression zone isin its natural state it has an unloaded outer diameter (D_(O1)) and anunloaded inner diameter (D_(I1)), and wherein when the compression zoneis reduced, the locking ring has a loaded outer diameter (D_(O2)) and aloaded inner diameter (D_(I2)).
 5. The pedicle screw according to claim3, wherein the tulip head includes a retention groove inlet that isconnected to the retention groove and extends to an exterior surface ofthe tulip head opposite the interior wall.
 6. The pedicle screwaccording to claim 5, wherein the locking ring is disposed in theretention groove inlet.
 7. The pedicle screw according to claim 6,wherein the locking ring is a wire fabricated from a material selectedfrom a group consisting of metals, alloys, and composites.
 8. Thepedicle screw according to claim 1, wherein the rod seat includes aretention ledge engageable with the stop.
 9. The pedicle screw accordingto claim 1, wherein: the rod seat includes a pair of retention ledges;and the tulip head includes a pair of arms defining a U-shaped channeltransverse to the cavity, the pair of arms defining the stop of thecavity of the tulip head.
 10. The pedicle screw according to claim 9,wherein the retention ledges are engageable with the arms to therebyprevent rotation of the rod seat relative to the tulip head.
 11. Apedicle screw comprising: a tulip head having an upper opening disposedin a top end of the tulip head and a lower opening disposed in a bottomend of the tulip head opposite the upper opening, wherein: the upper andlower openings form a single cavity extending through the tulip headfrom the top end to the bottom end, and the cavity has an interior wall,internal threads disposed within the interior wall and adjacent to theupper opening, and a stop disposed between the lower opening and theupper opening, the stop extending inwardly from the interior wall andseparate from the internal threads; a rod seat disposed within thecavity and engageable with the stop, the rod seat having a rod matingface, a shank mating face opposite the rod mating face, and a holedisposed through the rod mating face and shank mating face; a screwshank having a thread disposed along a length of the screw shank and aconnector positioned at an upper end of the screw shank; a retainercollar having a collar body, a pass through aperture disposed throughthe collar body, an anti-rotation tab extending from the collar body,and a collar expansion split disposed within the collar body, whereinthe retainer collar is disposed about the connector of the screw shank;and wherein the cavity of the tulip head further includes ananti-rotation socket constructed to receive and engage the anti-rotationtab of the retainer collar.
 12. The pedicle screw according to claim 11,wherein: the cavity of the tulip head has a retention groove disposedwithin the interior wall; the stop is disposed between the retentiongroove and the upper opening; and the retainer collar has a locking ringgroove disposed within an outer surface of the collar body.
 13. Thepedicle screw according to claim 12, further comprising a locking ringdisposed within the retention groove and the locking ring groove. 14.The pedicle screw according to claim 13, wherein the locking ring has acompression zone disposed therein such that when the compression zone isin its natural state it has an unloaded outer diameter (D_(O1)) and anunloaded inner diameter (D_(I1)), and wherein when the compression zoneis reduced, the locking ring has a loaded outer diameter (D_(O2)) and aloaded inner diameter (D_(I2)).
 15. The pedicle screw according to claim13, wherein the tulip head includes a retention groove inlet that isconnected to the retention groove and extends to an exterior surface ofthe tulip head opposite the interior wall.
 16. The pedicle screwaccording to claim 15, wherein the locking ring is disposed in theretention groove inlet.
 17. The pedicle screw according to claim 16,wherein the locking ring is a wire fabricated from a material selectedfrom a group consisting of metals, alloys, and composites.
 18. Thepedicle screw according to claim 11, wherein the rod seat includes aretention ledge engageable with the stop.
 19. The pedicle screwaccording to claim 11, wherein: the rod seat includes a pair ofretention ledges; and the tulip head includes a pair of arms defining aU-shaped channel transverse to the cavity, the pair of arms defining thestop of the cavity of the tulip head.
 20. The pedicle screw according toclaim 19, wherein the retention ledges are engageable with the arms tothereby prevent rotation of the rod seat relative to the tulip head.